The invention relates to ink jet printing devices and more particularly to ink jet printers using a replaceable printhead assembly with replaceable ink tanks and a monitoring system to record and display an out of ink condition for an ink tank depleted of ink. The monitoring system monitors the volume of ink remaining in the ink tank by accumulatively counting the droplets ejected and comparing the counted droplets to the predetermined number representative of the total ink volume in the ink tank. When an ink tank has been replaced before it has been depleted of ink by a new ink tank, the monitoring system detects the replacement and resets the accumulative droplet count to zero.
For the convenience of the users or customers of ink jet printers, customer replaceable printheads are used which may be removed and replaced by the customer when the printhead's design lifetime has expired. The customer replaceable printheads also use customer replaceable ink supply tanks or cartridges, and each printhead may deplete ink from many ink tanks before reaching the end of its design lifetime. For existing multicolor ink jet printheads, it is not uncommon for the printhead to deplete the ink from as many as ten ink tanks for each color of ink, for example, yellow, magenta, cyan, and black, before reaching the end of the printhead lifetime. It is known that the droplet-ejecting heating elements of thermal ink jet printheads have a lifetime determined by the number of times the heating elements are pulsed with an electrical signal and that a printer controller can determine the lifetime status of the printhead by accumulatively counting the number of times the heating elements are pulsed. It is also known that the ink volume remaining in the ink tanks can be determined by counting the number of ink droplets that have been ejected and replenished from a particular ink tank, because the volume of each ink droplet is substantially the same.
A problem of determining the available ink for a printhead is encountered when an ink tank is removed prior to ink depletion and a new ink tank installed, unless there is an optical low ink sensing system, which is expensive if not complex. In this situation, the printer counts the ink droplets until the predetermined number representing a depleted ink tank is reached and the printer thinks the ink tank is empty when in fact the ink tank still has usable ink. To prevent printhead damage caused by energizing heating elements in channels without ink, the printer controller stops the printer from printing until a new ink tank replaces the ink tank that the printer thinks is empty. Therefore, an ink tank with some ink still therein, must be removed and replaced by a new ink tank. This invention is directed to a cost effective way for the printer controller to monitor and keep track of the amount of ink remaining in the ink tank presently installed in the printer.
U.S. Pat. No. 4,961,088-A discloses a system for monitoring customer replaceable cartridges in printers or copiers. Each replaceable cartridge includes an electrically erasable programmable read only memory (EEPROM) which is programmed with a cartridge identification number that when matched a cartridge identification number in the printer or copier enables the printer or copier to operate, provides a cartridge replacement warning count, and provides a termination count at which the cartridge is disabled from further use. The EEPROM is programmed to store updated counts of the remaining number of images or prints available by the cartridge after each print or copy is made by the printer or copier.
U.S. Pat. No. 5,021,828-A discloses a replaceable unit for use in a copier or printer in which initial use and near-end-of-life is recorded by electrical means, including a portion itself removable from the removable, comprising two fuses. A first fuse is blown when a few copies have been made with the replaceable unit, and the second fuse is used to prevent further use of the replaceable unit when a certain number of copies or prints have been made with the replaceable unit.
U.S. 5,283,613-A discloses a monitoring system for replaceable cartridges in a printer or copier, including an electronic count memory and an electronic flag memory. The count memory maintains a one-by-one count of prints made with the cartridge. The flag memory includes a series of bits which are alterable from a first state to a second state but not alterable from the second state to the first state. The bits in the flag memory are altered at predetermined intervals as prints are made with the cartridge. The flag memory is used as a check to override unauthorized manipulation of the count memory.
U.S. 5,365,312-A discloses replaceable ink reservoirs, ribbon cassettes, or toner cartridges having an electronic memory means in the form of a chip in which information is stored about the current fill status of the reservoir and other status data that are relevant for printer operation. The used status of the ink or other printing medium is acquired from the controller of the printing machine and is communicated to the chip. The chip on the reservoirs counts consumption until the supply is exhausted to such an extent the reservoir must be replaced. A reprogramming of the chip and refilling of the reservoir is not possible.
U.S. Ser. No. 08/941,910 filed Oct. 1, 1997 and entitled "Printhead Assembly With Integral Lifetime Monitoring System" to Walter F. Wafler discloses an ink jet printer having a customer replaceable printhead assembly with a usage monitoring system which detects and displays the remaining available use or lifetime for the printhead assembly installed in the printer. The droplet ejecting electrical pulses applied to selected heating elements of the printhead in the printhead assembly are counted and compared with the number of pulses assigned to a set of permanently inactivable or changeable cell sites integral with the printhead assembly. Each time the number of counted pulses are equal to the value assigned for a cell site, the cell site is addressed to change its state from active to inactive. The remaining active cell sites are representative of the percent of remaining available use for the installed printhead assembly, and this percentage is displayed for the convenience of the customer. Because the cell sites are permanently changed, the supplier can also determine the amount of use of the printhead assembly when warranty claims are submitted.